module type ME = sig
  type 'a t
  val vide : unit -> 'a t
  val inserer : 'a -> 'a t -> 'a t
  val compter : 'a -> 'a t -> int
  val retirer : 'a -> 'a t -> 'a t
  exception Element_absent
end

module Util_ME = functor (M : ME) ->
struct
  let vide = M.vide
  let inserer = M.inserer
  let compter = M.compter
  let retirer = M.retirer

  let present = fun x e ->
    M.compter x e > 0
      
  let rec eliminer = fun x e ->
    try let e' = M.retirer x e in eliminer x e'
    with
    | M.Element_absent -> e
end

(***
#load "multiens.cmo";;
#load "multiens2.cmo";;
***)

module M = Util_ME(Multiens)

let e1 = M.inserer 'a' (M.inserer 'b' (M.inserer 'a' (M.vide ())))

let () = print_int (M.compter 'a' e1)
let () = print_int (M.compter 'b' e1)
  
let e2 = M.eliminer 'a' e1

let () = print_int (M.compter 'a' e2)
let () = print_int (M.compter 'b' e2)

let () = print_newline ()

module M' = Util_ME(Multiens2)

let e1 = M'.inserer 'a' (M'.inserer 'b' (M'.inserer 'a' (M'.vide ())))

let () = print_int (M'.compter 'a' e1)
let () = print_int (M'.compter 'b' e1)
  
let e2 = M'.eliminer 'a' e1

let () = print_int (M'.compter 'a' e2)
let () = print_int (M'.compter 'b' e2)